Usher syndrome is a rare disorder among the general population. However, among those who are deaf-blind, Usher syndrome is the most common genetic (inherited) cause of deaf-blindness. Recent studies estimate that between 8 and 10% of all individuals who are congenitally deaf or hard of hearing have Usher syndrome. There are three main types of Usher syndrome. Individuals with Usher will have hearing loss and a visual condition called retinitis pigmentosa (RP).
Retinitis pigmentosa is a progressive visual condition. The first symptom may be difficulty seeing at night (night blindness) or in poorly lit or dark environments such as hallways, movie theatres or in any outdoor venue at dusk or during the evening, when lighting is poor. The individual with RP is often unaware that they have this condition until their vision loss has progressed significantly. As children or young adults, they may be labeled "clumsy" or "accident prone," since, due to their night blindness, they bump into people and things in darkened environments. Along with night blindness, RP also causes a loss of peripheral, or side, vision. Whereas individuals with "typical" visual fields can see to their left and right--approximately 180 degrees--individuals with RP gradually lose their side vision. At the later stages of vision loss, their visual fields are such that it is like looking at the world through a tunnel - thus the term "tunnel vision." This impacts their ability to see people and objects to the far left and right, which may cause them to appear to others as disinterested, absent minded or careless. The slow and progressive nature of the loss of peripheral vision often causes individuals with RP to be unaware of this loss until their visual fields are quite restricted. They may quite naturally and intuitively adapt to this loss of peripheral vision by deliberately scanning their environment before proceeding.
Along with RP, each type of Usher syndrome has an accompanying hearing loss. Those with Usher I are born profoundly deaf and experience balance problems. Prior to the availability of cochlear implants, many children with Usher I attended schools for the deaf and eventually became part of the Deaf community. American Sign Language was, for many, their primary language. As night blindness and the loss of peripheral vision slowly progressed, their ability to receive signed information was seriously impacted.
Individuals with Usher II are born hard of hearing with RP. As children, they may use hearing aids and lipreading to assist with oral/aural communication. As their vision loss progresses, they may experience difficulty with lipreading in darkened environments. Some individuals perceive this as an additional loss of hearing, when it is actually the effect of the progressive loss of vision. Usher II does not have balance problems associated with it.
Usher III is quite rare, although there are a few cases diagnosed in the U.S. Hearing loss manifests in the mid teens or early 20s. This hearing loss is progressive. RP is usually diagnosed in the mid teens. Progressive balance problems are associated with type III.